Polyolefins have been chlorinated in the past. Randomly chlorinated polyethylenes (e.g. Tyrin.TM. from Dow Chemical) have been used in PVC or CPVC blends, generally as a processing aid and impact modifier. The chlorinated polyethylenes used in PVC or CPVC blends have been randomly (relatively homogeneously) chlorinated by using a swelling solvent and/or a chlorinating temperature above the crystalline melting temperature of the polyethylene. Traditionally those who chlorinated polyethylene wanted to eliminate the crystalline polyethylene phase by chlorinating the crystallizable polyethylene segments, which inhibits or prevents further crystallization of the polyolefin. Residual crystalline fractions in a chlorinated polyethylene would require a processing temperature above the melting point while amorphous polyethylene fractions can be processed at a lower temperature. The use of higher chlorination temperatures and swelling solvents (which decrease residual crystallinity) also increase the rate of the chlorinating reaction, thus reducing costs. It has even been postulated that highly crystalline polyethylene would not be effectively chlorinated unless either it was heated above the crystalline melting temperature or the crystallinity was reduced by using a swelling solvent.
Two articles were published in Polymer Engineering and Science, vol. 28 pp. 1167-1172 and 1173-1181, which tried to compare and contrast homogeneously chlorinated polyethylene and their blocky chlorinated polyethylene. The chlorination time for the blocky chlorinated polyethylene was continued through 20 hours. The authors postulated that during chlorination the crystalline polyethylene surfaces were chlorinated, converting them to amorphous chlorinated material. They observed that the melting point of the crystalline polyethylene was a function of crystalline thickness and the heat of melting (.DELTA.H) of the polyethylene decreased after about 20 wt. % chlorine was added. The crystalline thickness was limited after chlorination by the number of successive non-chlorinated methylene repeat units.
Various conventional impact modifiers have been used with PVC and CPVC such as ABS or MBS impact modifiers. Use of these impact modifiers can reduce other desirable properties of the PVC or CPVC such as heat distortion temperature, thermal stability, oxidation resistance, tensile strength and stability to ultraviolet (UV) light exposure. There have been neither publications nor commercial products (except for graft copolymers) that disclose or include polymers prepared by polymerizing blocks of two different monomers to use to compatibilize PVC or CPVC with polyolefins. There is a continuing need for a copolymer to improve the interaction of PVC and/or CPVC with polyolefin elastomers.